Surveying tibial trials for knee arthroplasty

ABSTRACT

A system and process for performing orthopedic surgery is provided that uses a tibial trial system in total knee arthroplasty for assessing optimal internal-external rotation and posterior tibial slope, and for measuring the rotation of a tibial trial throughout flexion-extension to determine and mark the best position for the final tibial component. The tibial trial system determines the internal-external location on a patient specific basis with improved component placement well within the present manual methods. One particular advantage to the tibial trial system is to assess the natural internal-external rotation that the tibial component will experience relative to the femoral component during flexion-extension as opposed to simply recording and balancing forces on a static tibial trial. The invention disclosed herein may also be adapted to be used with a computer assisted surgical device. Such surgical devices include active, semi-active, and haptic devices as well as articulating drill and saw systems.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority benefit of U.S. Provisional ApplicationSer. No. 62/090,660 filed 11 Dec. 2014; the contents of which are herebyincorporated by reference.

FIELD OF THE INVENTION

The present invention relates generally to the field of jointreplacement, and more specifically to a new and useful method forperforming tibial trials used to survey internal-external rotation andposterior slope to optimize final tibial component positioning in kneearthroplasty.

BACKGROUND OF THE INVENTION

Total joint replacement (TJR) (also called primary total jointarthroplasty) is a surgical procedure in which the articulating surfacesof a joint are replaced with prosthetic components, or implants. It is asuccessful procedure, especially for hips, knees, shoulders, and anklesand allows people to restore functionality while greatly reducing painassociated with osteoarthritis.

Bone is a living tissue that is constantly changing through theresorption of matrix by osteoclasts and the deposition of new matrix byosteoblasts. Articular cartilage is an avascular tissue that is found onthe surfaces of joints and serves to provide a smooth interface uponwhich bones can articulate with each other. Joint replacementarthroplasty is an orthopedic procedure in which the typically wornsurface of the joint is replaced with a prosthetic component, orimplant. Joint replacement arthroplasty typically requires the removalof the articulating cartilage surface of the joint including a varyingamount of bone depending on the joint and the replacement implant beingused. The articulating cartilage surface and bone is then replaced witha synthetic, typically metal implant that is used to create a new jointsurface.

The correct placement of the femoral and tibial components in total kneearthroplasty has a direct impact on clinical outcomes and implantlongevity. One particularly difficult placement parameter is theinternal-external rotation of the tibial component on the tibia.Rotational malpositioning of the femoral or tibial component may resultin flexion instability, component wear, deviated patellar tracking, andinadequate unsatisfactory joint kinematics, and pain.

During a conventional total knee arthroplasty, either with manualinstruments or via computer navigation, a tibial trial component is usedprior to implantation of the final tibial component. The tibial trialcomponent is used to verify the size of the final component and toensure the desired flexion-extension gap and ligament balancing has beenachieved. To determine the correct internal-external rotation of thefinal component, two methods are commonly used. One method references ananatomical landmark whereby the component is aligned with the midsulcusof the tibial spine, the posterior condylar line of the tibia, themedial border of the tibial tubercle, or the medial ⅓ of the tibiatubercle. Another method allows the tibial trail to freely rotatethroughout flexion and extension. The component is then aligned with theanterior position of the trial in extension and another reference point(e.g., center of tibia, posterior cruciate ligament (PCL)) on the tibia.However, clinical studies have shown that the final internal-externalrotation of the component has a large patient intervariability usingeither method. In the first method, the tibial trial is fixed to thetibial plateau, making it difficult to determine the best axial rotationof the component. The anatomic landmarks used to identify the correctinternal-external rotational alignment are also difficult to locateintraoperatively. The second method lacks in assessing the full range ofinternal-external rotation throughout flexion-extension.

Additionally, during knee arthroplasty, the posterior slope of thetibial cut is determined prior to using the provisional component, whichmakes it difficult to determine how much adjustment, if any, is neededin this degree of freedom. The final posterior tibial slope can have asignificant impact on clinical outcomes, joint stability, jointkinematics, and implant longevity. Traditionally, the surgeon will tryto restore the patient's natural slope and use a provisional componentto ensure the ligaments are balanced. In some circumstances, the slopeneeds to be re-cut after the trial has been used, and the degree ofangulation is determined based on the surgeon's judgment. However,because the tibia has already been cut, it can be difficult to determinehow much angulation, if any, is needed when performing a recut of thetibia.

Therefore, there is a need for a tibial trial component that can assista surgeon in consistently placing the final tibial implant component inthe proper internal-external rotation. There is an additional need for atibial trial component that can provide a surgeon with a quantitativemeasurement of a posterior tibial slope re-cut. There is a further needfor a method to mark or assist with the proper positioning of the finalcomponent as determined by the tibial trial.

SUMMARY OF THE INVENTION

A tibial trial system is provided that includes a base component havingan upper surface and a lower surface, and an articulating componenthaving a superior surface and an inferior surface. The base component isconnected to the articulating component by a rotary joint extending fromthe upper surface of the base. The upper surface of the base has atleast one rotation sensor positioned thereon, where the rotary joint isengaged with the inferior surface of the articulating component so thatthe articulating component can rotate relative to the base component.

A method of using the tibial system is also provided that includes usinga set of position marks generated by a computer assisted device todetermine a placement position for the tibial trial component in apatient's knee joint. The tibial trial component is inserted in thedetermined placement position. A rotational position of the articulatingcomponent is registered to the base component, and the knee joint isarticulated through flexion-extension, where the articulating componentrotates with a femoral component and a series of measurements are madeby the computer assisted device, where the computer assisted devicerecords and determines an optimum internal-external rotation relative tothe base component. Subsequently, the tibial trial component is removedto allow the computer assisted device to mill a keel hole for a finaltibial component placement in the determined optimum internal-externalorientation.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter that is regarded as the invention is particularlypointed out and distinctly claimed in the claims at the conclusion ofthe specification. The foregoing and other objects, features, andadvantages of the invention are apparent from the following detaileddescription taken in conjunction with the accompanying drawings inwhich:

FIGS. 1A and 1B generally illustrate two perspective views of a tibialtrial system in accordance with an embodiment of the present invention;

FIG. 2 depicts the tibial trial system depicted in FIGS. 1A and 1B withadditional axial holes for marking the final tibial component inaccordance with an embodiment of the invention;

FIGS. 3A and 3B depict a perspective (FIG. 3A) and cross-sectional (FIG.3B) view of the tibial trial system with coronal holes for marking thefinal tibial component in accordance with an embodiment of theinvention;

FIG. 4 illustrates an on-board display of the tibial trial system inaccordance with an embodiment of the invention;

FIG. 5 is a flowchart outlining steps to use the tibial trial systemwith a computer assisted surgical device in accordance with anembodiment of the invention; and

FIG. 6 is a perspective view of a tibial trial system configured with arotary joint in accordance with an embodiment of the invention, wherenon-visible surfaces are shown in ghost.

DESCRIPTION OF THE INVENTION

The invention disclosed herein describes a tibial trial system in totalknee arthroplasty for assessing optimal internal-external rotation andposterior tibial slope, but more particularly for measuring the rotationof a tibial trial throughout flexion-extension to determine and mark thebest position for the final tibial component.

It is to be understood that in instances where a range of values areprovided that the range is intended to encompass not only the end pointvalues of the range but also intermediate values of the range asexplicitly being included within the range and varying by the lastsignificant figure of the range. By way of example, a recited range from1 to 4 is intended to include 1-2, 1-3, 2-4, 3-4, and 1-4.

The invention disclosed herein has utility in assisting a surgeon tolocate and mark on the tibia the optimum internal-external rotation fora final tibial implant with respect to the femoral implant in total kneearthroplasty. It should be appreciated that the tibial trial system maydetermine the internal-external location on a patient specific basiswith improved component placement well within the present manualmethods. One particular advantage to the tibial trial system is toassess the natural internal-external rotation that the tibial componentwill experience relative to the femoral component duringflexion-extension as opposed to simply recording and balancing forces ona static tibial trial.

The invention disclosed herein may also be adapted to be used with acomputer assisted surgical device. Such surgical devices include active,semi-active, and haptic devices as well as articulating drill and sawsystems. Generally, pre-operative planning allows a user to plan a totalknee arthroplasty case and transfer the plan to the computer assistedsurgical device. The device may then aid the surgeon in making theappropriate cuts on the femur and tibia to match the pre-operative plan.However, the internal-external rotation of the component is stillplanned based on anatomic landmarks as seen on either two-dimensionalradiographs or three-dimensional bone models. It will be appreciatedthat the disclosed invention in conjunction with a computer assisteddevice may greatly improve the final tibial implant position in terms ofexternal-internal rotation and tibial slope.

Referring now to the figures, FIGS. 1A and 1B generally show a tibialtrial system 101 in accordance with embodiments of the invention. Themain components in the specific embodiment of the tibial trial system101 include an articulating component 103, a base component 105, arotary joint 107, and at least one rotational sensor 109 between thearticulating component 103 and the base component 105. The rotary joint107 is connected to the base component 105 and to the tibial traycomponent at engagement hole 111 so the articulating component 103 canrotate relative to the base component 105. The base component 105 alsohas at least one anchoring mechanism 113 to attach to the tibial plateauof a patient.

The rotary joint 107 connects the articulating component 103 to the basecomponent 105. In one embodiment the rotary joint 107 connects thearticulating component 103 and base component 105 at their geometriccenters. The rotary joint 107 can be any mechanism that allows thearticulating component 103 to rotate relative to the base component 105.In one embodiment, the rotary joint 107 is rigidly fixed to the basecomponent 105 and to the articulating component 103, whereby therotation occurs on the rotary joint 107 between the articulatingcomponent 103 and the base component 105. In another embodiment therotary joint 107 is fixed to the base component 105, and the rotaryjoint 107 attaches to the articulating component 103 whereby therotation occurs between the connection between the rotary joint 107 andthe articulating component 103. In an alternative embodiment the rotaryjoint 107 is fixed to the articulating component 103 and attaches to thebase component 105 whereby the rotation occurs between the connectionbetween the rotary joint 107 and the base component 105.

The base component 105 attaches to the tibial plateau of the patientafter the surgeon has made the tibial cut. In one embodiment, the basecomponent 105 has two small protrusions 113 that can fit into twocomplimentary holes made on the tibial plateau of the patient. Thereforethe base component 105 is fixed to the tibial plateau in a designatedspot. The articulating component 103 may then rotate with the femoraltrial component on the femur during flexion-extension of the knee toassess component sizing, flexion-extension gap, ligament balancing andinternal-external rotation. In one embodiment, the tibial trial system101 is assembled as one unit. In another embodiment, there are multiplearticulating components that the surgeon can choose from. For example,different sizes, shapes, slopes, etc. of the articulating component maybe assembled onto the base component intra-operatively to assess thefinal tibial component size, flexion-extension gap, ligament balancing,etc. The components 103 and 105 are readily formed of materialsconventional to orthopedic surgical aids, these materials illustrativelyinclude plastics, steel, aluminum, or brass. It is appreciated that aplastic component is readily formed so as to be transparent to providefor visual inspection of underlying surfaces.

At least one rotation sensor 109 is integrated between the articulatingcomponent 103 and the base component 105. The rotation sensor/s 109 maybe attached to or within the articulating component 103, the basecomponent 105, rotary joint 107, or any combination thereof. Therotation sensor/s 109 may be any sensor capable of measuring rotationsuch as but not limited to a potentiometer, Hall Effect sensor, encoder,rotary variable differential transformer, resolver, etc. The rotationsensor/s 109 measures the amount of rotation that occurs between thebase component 105 and the articulating component 103. In oneembodiment, once the tibial trial 101 is positioned on the patient'stibial plateau and the knee is placed in full extension, the sensor 109is zeroed. The surgeon then articulates the knee throughflexion-extension and the sensor 109 measures and records the anglebetween the articulating component 103 and the base component 105. Atleast one processor (not shown) may be incorporated with the tibialtrial system 101 to process the rotational data. In another embodiment,the tibial trial system 101 incorporates at least one memory storageunit (not shown) to store the rotational data. The tibial trial system101 may also include a mechanism to lock the articulating component 103in a desired internal-external rotation. The user may then assess theknee in flexion and extension with the articulating component 103 lockedin the desired internal-external rotation.

In one specific embodiment, the data is sent to an external device by aphysical wired or wireless connection. The external device could be forexample a computer, a monitor, a computer assisted surgical device, anoptical tracking system, a smart phone, heads up display (HUD) unit,glasses (such as Google glasses), etc., and any combination thereof. Thephysical connection could be by any electrical means connected to thetibial trial system 101 and to the external device. The data could besent wirelessly from a transmitting device (not shown) on the tibialtrial system 101 in communication with the rotation sensor/s 109 and/orprocessor/s incorporated with the tibial trial system 101. The datacould be sent wirelessly for example via Bluetooth, Internet connection,radiofrequency, electromagnetic, visible light, targeted visible light,infrared, etc. In the case of transmitting data using visible light, inone embodiment, the tibial trial system 101 may incorporate active lightemitting diodes (LEDs) in communication with the processor/s and/orrotation sensor/s 109.

In another embodiment, with respect to FIG. 4, the rotational data 403may be read from a display 401 incorporated with the tibial trial system101. The display 401 may be incorporated on the articulating component103 and/or the base component 105. The types of rotational datadisplayed and/or sent to an external device may include for example therotational range, a mean value, a median value, etc. that indicates anoptimum internal-external rotation for the final tibial component. Inone embodiment, the user may select what information is displayed on thedisplay unit 401.

Once a value has been indicated to the surgeon as to the optimuminternal-external rotation placement, the tibial trial system 101 mayhave features to allow the surgeon to mark the position for the finalcomponent. In one embodiment, with respect to FIG. 2, the articulatingcomponent 103 has at least one hole 201, and the base component 105 hasat least one corresponding groove 203. The groove 203 having asemi-circular or circular design to correspond with the rotation of thehole 201 as the articulating component 103 rotates relative to the basecomponent 105. Therefore, the surgeon may mark on the tibial plateau atany rotation of the articulating component 103. In one embodiment, thespacing or geometry of the hole/s 201 and groove/s 203 is unique to aspecific line of manufactured final tibial components so the markingswill easily align to correctly place and/or prepare the keel for thefinal tibial component.

If the holes 201 are positioned as shown in the example of FIG. 2 for anembodiment of the tibial trial system 200, the surgeon may have to gainaccess to the holes 201 by flexing and/or distracting the knee or evenremove the femoral trial component. In this embodiment, once the surgeonhas access to the holes 201, the surgeon may rotate the articulatingcomponent to the optimum internal-external external rotation that wasdetermined during the trialing. The angle or rotation of thearticulating component can be displayed an external device or the tibialtrial system display 401, and once the angles or rotation have matchedthe optimum internal-external rotation, the surgeon can mark the tibialplateau through the hole/s 201 and groove/s 203.

In an embodiment of the tibial trial system 300, with respect to FIGS.3A and 3B, the hole/s 301 and groove/s 303 are positioned to allow thesurgeon to mark the tibial plateau without having to flex, distractand/or remove the femoral trial component. The holes 301 are positionedon the front of the articulating component 103 and the grooves 303 ofthe base component 105 are angled to provide access to mark the tibialplateau. The grooves 303 likewise are semi-circular and/or circular tocorrespond with the holes 301 as the articulating component 103 rotatesrelative to the base component 105. FIG. 3B depicts a cross sectionalview at 305 of the tibial trial system illustrating the access thesurgeon has to mark the tibial plateau. In one embodiment, the spacingor geometry of the holes 301 is unique to a specific line ofmanufactured final tibial components so the markings will easily alignto correctly place and/or prepare the keel for the final tibialcomponent.

Tibial Posterior Slope

During the preparation of the tibial plateau, the posterior tibial slopecut is performed before trial reduction. A tibial trial system 101 mayalso include a rotary joint that allows for incremental changes in theamount of tibial posterior slope. The tibial trial system similarly hasan articulating component, a base component and at least one rotaryjoint connecting the two components. The trial system additionally has amechanism that allows the user to adjust the posterior slope duringtrial reduction. Before trialing, the slope may be set to a neutralposition corresponding to the initial tibial slope cut. Duringflexion-extension of the knee, the user may assess the laxity andstability and adjust the slope accordingly. For example, if the knee istight in extension then the surgeon can reduce the slope incrementallyto reduce tightness. If the knee is tight in flexion then the surgeoncan increase the tibial slope incrementally to reduce tightness. If thetibiofemoral joint dislocates, the tibial slope can be adjusted toimprove conformity of the posterior articular surface. When the surgeonis satisfied with the patient's range of motion, laxity, and stability,the surgeon reads the required change from an indicator and uses thatinformation to adjust the posterior slope.

The change in slope can be by any mechanical or electrical means thatallows for a change in slope. For example, a rotary joint may be rigidlyfixed to the base component 105 with a connection to the articulatingcomponent 103. Worm gears, hinges, screws, actuators, springs, bearings,ratchets, step motors, etc., may be assembled in a manner that allowsthe user to adjust the slope and maintain that slope throughout flexionand extension of the knee. An illustrative example is shown in FIG. 6.FIG. 6 is a perspective view of a tibial trial system 600 configuredwith a rotary joint in accordance with embodiments of the invention Ahinge joint 605 connects the base component 603 and the articulatingcomponent 601. An adjustable knob 609 may be used to incrementallyadjust and lock the slope of the articulating component 601 relative tothe base 603. A ratcheting mechanism (not shown) could be used to lockthe articulating component 601 in the desired slope. In one embodiment,springs 607 are attached between the articulating component 601 and thebase component 603 for added support during flexion and extension. Inanother embodiment, a step motor (not shown) may be placed inside thearticulating component 601 in connection with the hinge 605. The usermay adjust the slope electrically with controls on the trial system orfrom an external device in communication with the step motor.

The base component 603 of the tibial trial slope system may be smallerin shape than the articulating component 601. The smaller shape mayprovide a greater degree of total slope change for the articulatingcomponent 601. For example, the base component can be 10% to 99% of thesize of the articulating component 601 so the top of the base component603 does not interfere with the anterior, posterior, medial or lateraledges of the articulating component 601 as the user adjusts the slope.

In one embodiment, the user may manually adjust the slope using a dial,knob, wing nut, screw, etc. One turn or set amount of manual adjustmentcould result in an x degree of slope change. For example, a wing nutthat is rotated 180 degrees may result in a 1 degree change in slope. Inanother embodiment, the rotation may be done by pushing an up or downbutton whereby the slope change is controlled electronically. In oneembodiment, anterior portion and the posterior portion of the trialsystem may be adjusted independently. In another embodiment, the medialportion and lateral portion of the trial system may be adjustedindependently. Slope changes in the medial and lateral portion of thetrial system may allow a user to assess the varus and valgus of thepatient throughout flexion-extension and make any adjustments necessaryin this degree of freedom. The tibial trial system can be capable ofregistering the initial slope when the user installs the trial system.As the user changes the slope, the change in degrees may be sent by wireor wirelessly to an external device as explained above.

In another embodiment, the tibial trial system may both rotate relativeto the base as well as have the capability to change the slope.Therefore the tibial trial system would have two degrees of freedom inassessing the proper orientation of the final tibial component as wellas assess any changes needed for the posterior tibial slope. In oneembodiment, the tibial trial system is assembled as one unit. In anotherembodiment, multiple articulating components can be assembled onto thebase component to assess the proper size of the final tibial tray.

Computer Assisted Procedures

The tibial trial system 101 may similarly be used with a computerassisted surgical device to help aid in assessing the correctinternal-external rotation and tibial slope of the final tibialcomponent. With reference to FIG. 5, a computer assisted device may makethe holes for the tibial trial system 501. For example, holes that matchthe protrusion 113 of the base component on the tibial plateau. Theholes may be made based upon a pre-operative plan, registeredintra-operatively with for example a digitizer, or marked by anoptically tracked device. In one embodiment, the computer assisteddevice is an optically tracked articulating drill system that can markthe position of the holes on tibial plateau with the tip of the drill.The positions may then be registered with the tracking system relativeto the bone whereby the tracking system will then maintain thearticulating drill in the position to accurately mill the holes. Inanother embodiment, the computer assisted device is an active system.The active system may actively drill the holes for the tibial trialsystem 101 based upon a preoperative plan or communicated to the deviceusing registration techniques such as a mechanical or optical digitizer.

Once the holes have been milled, the user may place the tibial trialsystem onto the tibial plateau 503. The user then articulates the kneethroughout flexion-extension 505. The articulating component rotateswith the femoral component relative to the base component and theangular and/or rotational measurements are sent by wire or wirelesslyand read by external device 507. The external device processes the dataas to the optimum internal-external rotation and/or adjustments to thetibial slope 509. In one embodiment of the inventive system, the optimuminternal-external rotation and/or tibial slope adjustments is shown tothe user for confirmation. After trialing, the computer assisted devicemay mill the keel hole in the correct orientation to place the finaltibial component. In one embodiment, the computer assisted device iscapable of cutting the keel actively 511. In another embodiment, acomputer assisted device unable to make the cut may still mark thecorrect position on the tibial plateau whereby the user can then alignmanual instruments to make the correct keel hole in the properorientation.

Other Embodiments

While at least one exemplary embodiment has been presented in theforegoing detailed description, it should be appreciated that a vastnumber of variations exist. It should also be appreciated that theexemplary embodiment or exemplary embodiments are only examples, and arenot intended to limit the scope, applicability, or configuration of thedescribed embodiments in any way. Rather, the foregoing detaileddescription will provide those skilled in the art with a convenient roadmap for implementing the exemplary embodiment or exemplary embodiments.It should be understood that various changes can be made in the functionand arrangement of elements without departing from the scope as setforth in the appended claims and the legal equivalents thereof.

The invention claimed is:
 1. A tibial trial system comprising: a basecomponent having an upper surface and a lower surface; an articulatingcomponent having a superior surface and an inferior surface; a rotaryjoint extending from the upper surface of the base; at least onerotation sensor positioned on the upper surface, said rotary jointengaged with the inferior surface of said articulating component so thatsaid articulating component can rotate relative to the base component;and a lock to secure said articulating component in a desiredinternal-external rotation.
 2. The tibial system of claim 1 wherein saidrotary joint connects said articulating component and said basecomponent at their geometric centers.
 3. The tibial system of claim 1wherein said rotary joint is rigidly fixed to the base component and tosaid articulating component to induce rotation on said rotary joint. 4.The tibial system of claim 1 further comprising a plurality ofarticulating components that vary from one another in at least oneparameter of size, shape, slope so as to assess a final tibial componentsize, flexion-extension gap, or ligament balancing.
 5. The tibial systemof claim 1 wherein said at least one rotational sensor comprises atleast one of: a potentiometer, Hall Effect sensor, encoder, rotaryvariable differential transformer, or a resolver.
 6. The tibial systemof claim 1 further comprising at least one processor to process a set ofrotational data supplied from said at least one rotational sensor. 7.The tibial system of claim 1 further comprising at least one memorystorage unit to store the rotational data supplied from said at leastone rotational sensor.
 8. The tibial system of claim 1 wherein said atleast one rotation sensor provides rotational data to a displayincorporated on said articulating component or on said base component.9. A tibial trial system comprising: a base component having an uppersurface and a lower surface; an articulating component having a superiorsurface and an inferior surface; a rotary joint extending from the uppersurface of the base; at least one rotation sensor positioned on theupper surface, said rotary joint engaged with the inferior surface ofsaid articulating component so that said articulating component canrotate relative to the base component; and an aperture on at least oneof said superior surface or a front face of said articulating componentand a corresponding groove on said base component, said groove having asemi-circular or circular design to correspond with a rotation of saidaperture as said articulating component rotates relative to said basecomponent.
 10. The tibial trial system of claim 1 wherein said basecomponent further comprises at least one anchoring mechanism to attachsaid base component to a tibial plateau of a patient's tibia bone. 11.The tibial trial system of claim 10 wherein said at least one anchoringmechanism has two protrusions from said lower surface that can fit intotwo complimentary holes made on the tibial plateau of the tibia bone ofthe patient.
 12. The tibial system of claim 1 wherein said at least onerotational sensor provides a set of data via a wired or a wirelessconnection to an external device.
 13. The tibial system of claim 12wherein said external device comprises at least one of: a computer, amonitor, a computer assisted surgical device, an optical trackingsystem, a smart phone, a heads up display (HUD) unit, wearable displayglasses and headgear, or any combination thereof.
 14. The tibial systemof claim 12 wherein said wireless connection comprises at least one ofBluetooth, Internet connection, radiofrequency, electromagnetic, visiblelight, targeted visible light, or infrared.
 15. The tibial system ofclaim 14 wherein if said data is transmitted using visible light thensaid tibial system employs one or more active light emitting diodes(LEDs).
 16. A tibial trial system comprising: a base component having anupper surface and a lower surface; an articulating component having asuperior surface and an inferior surface; a rotary joint extending fromthe upper surface of the base; at least one rotation sensor positionedon the upper surface, said rotary joint engaged with the inferiorsurface of said articulating component so that said articulatingcomponent can rotate relative to the base component; and a rotary jointthat allows for incremental changes in the amount of tibial posteriorslope between said base component and said articulating component. 17.The tibial system of claim 16 wherein said rotary joint furthercomprises at least one of: worm gears, hinges, screws, actuators,springs, bearings, ratchets, or step motors; and wherein the slope ofsaid rotary joint is controlled by manually or electrically via anadjustment knob.
 18. A method of using a tibial trial system comprisinga base component having an upper surface and a lower surface; anarticulating component having a superior surface and an inferiorsurface; a rotary joint extending from the upper surface of the base;and at least one rotation sensor positioned on the upper surface, saidrotary joint engaged with the inferior surface of said articulatingcomponent so that said articulating component can rotate relative to thebase component, said method comprising: using a set of position marksgenerated by a computer assisted device to determine a placementposition for said tibial trial system in a patient's knee joint;inserting said tibial trial system in the determined placement position;registering a rotational position of said articulating component to saidbase component; articulating the knee joint through flexion-extension,where said articulating component rotates with a femoral component and aseries of measurements are made by the computer assisted device, wherethe computer assisted device records and determines an optimuminternal-external rotation relative to said base component; and removingsaid tibial trial component to allow the computer assisted device tomill a keel hole or mark a position for the keel hole for a final tibialcomponent placement in the determined optimum internal-externalorientation.